As an ideal tracer gas in atmospheric science, radon plays a crucial role in elucidating the mechanisms governing its atmospheric concentration, which holds significant research importance. This study conducted continuous radon monitoring in Beijing to investigate its diurnal and seasonal variations, as well as its correlations with meteorological factors. Radon concentration exhibits a characteristic diurnal cycle with daytime diffusion and nighttime accumulation, a pattern largely attributable to temperature inversion. Additionally, radon concentration exhibits cyclical variations every 5-10 days, corresponding to medium-term atmospheric circulation patterns. Average radon concentrations ranged from 5.61 to 8.71 Bq·m-3 in spring and summer, and from 7.71 to 11.86 Bq·m-3 in autumn and winter. Furthermore, a positive correlation exists between radon concentration and relative humidity, while a negative correlation is observed with ambient temperature. These correlations are weaker in spring and summer and stronger in autumn and winter. A 1 h lag in radon concentration changes is evident relative to both relative humidity and temperature, with the correlation reaching a maximum at this lag time. The results of this research enhance the understanding of atmospheric radon concentration dynamics and provide a solid scientific foundation for developing a short-term prediction model of radon levels based on meteorological parameters.

Radioxenon isotopes monitoring is of interest to the international monitoring system (IMS) of the comprehensive nuclear-test-ban treaty (CTBT). In the current IMS, the beta-gamma coincidence system utilizing plastic scintillator detectors and HPGe detectors achieves the best minimum detectable activity. PIPSBox detectors have outstanding advantages of higher energy resolution and a lower "memory effect", which may offer a new option for beta detectors in IMS. A dedicated high-resolution beta-gamma coincidence system has been developed in CNL06 referring to the Spalax next generation system. Commercial PIPSBox detector measurements with four radioxenon isotopes were performed at two different facilities with different background conditions.

Bayesian source reconstruction is important to trace the atmospheric radioactivity emissions in both unintended and accidental scenarios. The likelihood function is a key component of Bayesian reconstruction determining its performance. In this paper, Bayesian methods using different likelihood functions and parameterization schemes were evaluated based on the European Tracer Experiment (ETEX), including 27 different likelihood functions that involves the combination of Gaussian, log-Gaussian and log-Laplace functions and 9 parameterization schemes. 100 test data sets were randomly sampled from the observation network of ETEX and the 27 likelihoods were applied to each of the 100 data sets. The performances of 27 different likelihood functis were compared based on the posterior distributions of the reconstructed parameters in individual reconstructions and the statistical distribution of errors across the 100 tests using Nemenyi tests. Results show that likelihood functions have significant influence on source estimation. Gaussian likelihood is the most sensitive to the parameterization scheme. But it presents a good location accuracy, while the deviations are below 0.3 degrees, if appropriately parameterized. The log-Gaussian and log-Laplace likelihoods exhibit comparable reconstruction performance and show less sensitive to scale parameters than Gaussian likelihoods. The above information provides an insight into the reconstruction design and the parameterization in practical applications.

Four radioxenon isotopes are key radionuclides in nuclear explosions monitoring under the Comprehensive Nuclear-Test-Ban Treaty verification regime. Due to the high sensitivity of the (-gamma coincidence method, it is widely used in International Monitoring System radionuclide station equipment. Plastic scintillation detectors and HPGe detectors are one option, with some technological issues that need to be addressed. In this work, a plastic scintillation detector based on a silicon photomultiplier tube (SiPM) array readout is developed, and the essential performance is evaluated. The SiPM-based detector is compact and can be applied successfully to mixed radioactive xenon measurement.

Inversion for the radioactive source term has received growing attention in the post-Fukushima era. Under some special scenarios, the source term, including release rate, height and position, is necessary for nuclear emergency response and consequence assessment. Here, a transformer-based deep learning architecture was developed for multivariable source term estimation. The CALMET-LAPMOD coupling model validated by the Kincaid tracer experiment was employed to produce the datasets. The datasets were systematically constructed for five representative scenarios with the following time-varying parameters: release rate, release height, release location, coupling of release rate and height, and coupling of all three variables. Subsequently, a Transformer model with Bayesian optimization for adaptive hyperparameter tuning was developed. The results demonstrated excellent performance in source term inversion, with a determination coefficient (R2) of above 0.96 for release rate and height, and an average distance error of 1.19 km at a 95 % confidence level for location prediction. Regarding the coupling of all three variables scenario, the R2 for release rate and location remained above 0.92, whereas the height achieved R2 of 0.72. Additionally, feature ablation analysis revealed that monitoring points with high concentration values contribute significantly to inversion, providing quantitative insights to optimize the monitoring network layout.

A β-γ coincidence system for radioxenon measurement with high detection sensitivity has been developed in Beijing Radionuclide Laboratory by using a broad energy germanium γ-detector and a plastic scintillator β-detector. In order to further improve the performance of the system, a cosmic-ray veto detector system has been implemented to reduce the background induced by cosmic-ray muon. This paper reports on the setup and commissioning of the anti-cosmic β-γ coincidence system. In a 24-h measurement of the system, the Minimum Detectable Activity (MDA) for 131mXe, 133mXe, 133Xe and 135Xe have been estimated to be 0.9 mBq, 1.1 mBq, 2.2 mBq and 2.1 mBq respectively.

41Ar是反应堆和加速器运行释放到环境中的主要放射性核素之一，具有半衰期短的特点。由于β-γ符合法能显著降低本底、提高探测器灵敏度，为了实现41Ar高灵敏度测量，设计了由BC404和CsI(Tl)组成的β-γ符合闪烁体探测器，并建立了以最小可探测活度浓度（Minimum Detectable Activity Concentration，MDC）为优化目标的探测器结构优化方法。首先，运用Geant4对β射线在CsI(Tl)中的泄漏率进行模拟，选择BC404厚度为3 mm，此时泄漏率为0.73%；其次，对不同的气体腔尺寸进行模拟，分析计算β探测效率、γ峰效率、气体腔体积和取样时间对MDC的综合影响，完成探测器的结构优化；最后，分析了本底计数率和测量时间对MDC的影响。当测量时间为200分钟、处理时间为30分钟、本底计数率为5×10-3 cps时，优化后的探测器对41Ar的MDC估算值为1.7 Bq/m3。

As a passive nondestructive nuclear technique,gamma ray spectrometry is used in many radioactivity laboratories.Gamma-ray spectrometry enables the identification of radionuclides in a sample from their emitted photon energy and calculation of their activities from the number of photons collected for each energy.However coincidence summing effects will influence the reliability of both radionuclide identification and calculation of activity.Coincidence summing effects appear when sources emitting coincident gamma rays are measured via gamma-ray spectrometry.Those effects that result in losses from the full energy peaks and enhancement of sum peaks influence the accuracy of the spectral analysis.To eliminate this influence,many correction methods have been established.Research on the coincidence summing effect(CSE)originated in the 1960s.Subsequently,many algorithm-based generation mechanisms of CSE have been built together with the development of corresponding correction software.Massive amounts of technological information on and achievements about coincidence summing correction have been reported by researchers from different countries,hence several intercomparisons of these methods,and self-consistency testing of cascaded additive effect correction algorithm were organized by the International Committee for Radionuclide Metrology(ICRM).Based on a detailed summary of the development history of correction methods,the CSE mechanisms,correction algorithms,correction software,and application of correction techniques were reviewed in this paper.Cobalt-60 was taken as an example to illustrate the influence of the summing-in and summing-out effects,with correction equations based on different measurement geometries and considering the impact of angular correlations.Meanwhile,the performance of different algorithms and software were compared and analyzed.Combined with the current research status,some suggestions are presented for future research for domestic researchers on the coincidence summing effect correction.First,the efficiency must be accurately established for the geometrical conditions of the measurement.Second,the number of cascades in the algorithm must be taken into account owing to its influence on the results.Third,correction software with a user-friendly interface and database of accurate decay schemes should be developed.

Inert gas argon has important applications in the fields of daily life, industrial manufacture and nuclear environmental monitoring. The key to its application is to selectively and efficiently separate and purify Ar from complex gas components. However, the separation of O2 and Ar at normal temperature is full of challenge due to their similar molecular sizes and adsorption properties as well as their close boiling point. In industry, high purity Ar is mainly produced by low temperature rectification, which is mature technology, but the equipment is large, high-energy consumption and explosive. Adsorption separation is a common method of gas separation. Molecular sieves are the most widely used material due to their huge specific surface area, aboudant pore structure and excellent adsorption properties. The silica tetrahedron in molecular sieve is electrically neutral, while the aluminum tetrahedron is electronegative, which makes it necessary to use H+ or Na+ outside the molecular sieve skeleton to maintain electrical neutrality. In actual application, the interaction between adsorbent and adsorbent can be enhanced by ion-exchange modification of molecular sieve material, so as to effectively improve the O2/Ar separation capacity of molecular sieve. In this paper, the application of ion-exchange modified molecular sieve materials in the field of O2/Ar adsorption separation was systematically summarized and reviewed. The results show that the O2/Ar separation coefficients of molecular sieves modified by alkaline earth metal ions like Ca2+, Sr2+ and Ba2+ can reach about 2.0, while that of Ce3+-exchanged X-type molecular sieve is as high as 5.9, it is an ideal adsorption material for O2/Ar separation. However, the high separation coefficient is limited to the range of low partial pressure, and the O2/Ar separation coefficient under normal pressure is below 2.0. The Ag+-exchanged molecular sieves, namely silver-loaded molecular sieves, have excellent Ar adsorption selectivity. At present, the O2/Ar separation coefficients of silver-loaded molecular sieve materials at atmospheric pressure are around 2.0, but the preparation cost of silver-loaded molecular sieves is high, and it is more suitable for small-scale separation applications, it means that the efficient separation of O2 and Ar at normal temperature and pressure is still challenging. The development of novel ion-exchange modified molecular sieve materials with high adsorption capacity and high adsorption selectivity for the separation of O2 and Ar is still one of the focuses and trends of future research projects.

Measurement of the four relevant radioxenon isotopes, namely 131mXe, 133mXe, 133Xe, and 135Xe, play a key role in underground nuclear explosion monitoring for ensuring compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). A β-γ coincidence system that employs a plastic scintillator detector and a HPGe detector was developed in Beijing Radionuclide Laboratory. The Minimum Detectable Activity (MDA) in a 24-h measurement of the system for 131mXe, 133mXe, 133Xe and 135Xe can achieve 1.8 mBq, 1.4 mBq, 3.4 mBq and 4.1 mBq, respectively.

The efficient capture of trace xenon is one of the important technologies in the fields of nuclear-test ban verification, nuclear accident emergency response, and nuclear facility operation supervision. The key to efficient capture of trace xenon is the development of high-performance xenon adsorption materials. Focusing on the key technology of trace xenon capture, this paper summarizes the adsorption principle of trace xenon, and the research progress of xenon adsorption materials both at home and abroad. The advantages and disadvantages of carbon materials, zeolite molecular sieves, metal-organic frameworks materials, and other adsorption materials for trace xenon are compared and analyzed. Finally, based on the research status of trace xenon adsorption and trapping materials, the design and synthesis of polarized microporous materials is expected to be an important direction of trace xenon adsorption research.

85m Kr is an important gaseous fission product in nuclear security and nuclear arm control research fields. The half-lives of 85m Kr published in previous works are significant discrepancy. Over the last 50 years, no new half-life value of 85m Kr has been reported. The half-life of 85m Kr was re-determined with two high purity germanium (HPGe) detectors by position relay method. Data was recorded at regular time intervals during measurement in order to simplify the analysis of data. The determined half-life of 85m Kr is 4.504±0.011 hours based on four independent measurements, which agrees very well with the evaluated value within the uncertainty limits. The new half-life value is useful to clarify and reevaluate the discrepancy among previous literature values.

Measurement of the four radioxenon isotopes, namely 131mXe, 133mXe, 133Xe, and 135Xe, play a key role in underground nuclear test monitoring for ensuring compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). To improve detection sensitivity, a β-γ coincidence technique is commonly used. Due to the presence of the gas matrix, such as stable xenon, nitrogen, helium, the self-attenuation effects should be taken into account when measuring different types of sample. In order to improve the accuracy of the measurement, the detection efficiencies of X-rays and γ-rays were derived by using a simulation gas calibration source with low density of sponge matrix. The detection efficiencies of β-particles and conversion electrons (CEs) were calibrated by measuring radioxenon sample. The self-attenuation correction factors of X-rays and γ-rays were determined by Geant4 simulation method. The self-attenuation correction factors of β-particles and CEs were provided by measuring the radioxenon samples with different volumes of xenon, nitrogen and helium.

Radioxenon monitoring is one of the important methods used by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to detect a clandestine nuclear weapon test. Many radioxenon detection systems have been developed in the past few decades. The disadvantages such as bad energy resolution, memory effect, and large size influence the performance of these systems. This work introduces a new detection system that utilizes a PIPSCell and two CZT-Arrays for radioxenon monitoring. Signals from ten detectors are processed and coincidence events are identified via the electronics based on time-stamped list mode. This compact system has good radiation detection resolution at room temperature and high detection sensitivity for both electron and gamma-ray. Preliminary 137Cs and 131mXe are used to calibrate the energy and efficiency of the system. Combined with the simulation results the minimum detection activity of four radioxenon were assessed.

大气放射性氙是全面禁止核试验条约重要的监测目标,为提高氙样品的探测灵敏度,在进行放射性活度测量前,需将样品纯化、除氡并转移至测量容器.本文针对氙样品高效纯化制备过程中的关键技术,研究了氙在三级吸附柱上的吸附脱附行为,并考察了氙样品量及色谱参数对氙色谱峰宽的影响,确定了纯化制备流程参数.利用氙样品对纯化制备流程进行测试,氙的回收率大于90％,氡去污因子大于104,实现了放射性氙样品的高效纯化制备.

Four CTBT relevant radioxenon isotopes, namely (131)mXe, (133)mXe, Xe-133 and Xe-135, play a key role for underground nuclear test monitoring. In order to improve the detection sensitivity of radioxenon, a plastic scintillator detector, which was used as the detector as well as the gas sample cell, was developed. Then the performances of the plastic scintillator detector were tested. The hermetic seal was quite good with the leakage rate less than 1x10(-4)Pa.L/s. The energy resolution of 129.4 keV conversion electron associated with (131)mXe was determined to be 27%. A significantly high detection efficiency of-particle was achieved. The detection efficiencies of 346.4 keV -particle for Xe-133 and 129.4 keV conversion electron for (131)mXe are 0.966 +/- 0.029 and 0.988 +/- 0.005 respectively. The memory effect was found to be less than 3%. The plastic scintillator detector provides adequate foundation of beta-gamma(HPGe) coincidence measurement method research of high resolution and high sensitivity.

研究碳分子筛的大气氩氪氙富集、浓缩与纯化行为,并结合膜分离技术,建立了一套大气中氩、氪、氙综合取样技术方案和取样流程,实现了氩、氪、氙样品的高效获取.结果 表明,13 h氙实际获取量5.2 mL,氪获取量15.2 mL,氩获取量392 mL.

The dispersion timeline and the specific ratio characterization of airborne radionuclides released from the Fukushima Daiichi Nuclear Power Plant accident were investigated based on an analysis of the monitoring data obtained from regional stations and radionuclide stations of the International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty. The comprehensive temporal sequence of airborne radionuclide arrival time at different sites was given, including xenon, iodine, and cesium isotopes, which could be used to validate and evaluate atmospheric transport modeling. Based on the decay time estimation method, the release time and process of radionuclides were calculated and analyzed through activity ratios of I-133 to I-131, Cs-136 to Cs-137, and Cs-134 to Cs-137. It indicated that radioiodine isotopes leaked from the reactors in the early stage after the 2011 Great East Japan Earthquake occurred, and there were two sources which leaked radiocesium, one is units 1, 2, and 3 of the Fukushima Daiichi NPP and the other is the spent fuel pools with a high possibility. Generally, this study provides some valuable findings and information for further evaluation of the accident and relevant research work.

本文介绍了全面禁止核试验条约(CTBT)筹委会临时技术秘书处(PTS)组织的2003年度国际放射性核素实验室能力验证过程.PTS在真实核试验监测数据基础上,通过模拟产生了2003年度能力验证活动的参考γ能谱,能谱中添加了24种裂变产物、5种活化产物和5种天然放射性核素.北京放射性核素实验室分析出了其中的27种核素,核素活度及其活度浓度分析结果与参考值在不确定度范围内一致.利用95 Zr和95 Nb活度比计算了核事件的零时,与参考值仅相差0.26 d.根据参考谱中裂变产物和活化产物信息,指出裂变产物应主要由238 U和239 Pu裂变产生,参考谱应源自真实核试验的监测数据.